The present invention relates to a method for enhancing the life of a downstream part disposed in a gas stream into which a cooling medium is injected through orifices of a first part upstream of the second downstream part.
The life of parts exposed in a hot gas stream is very sensitive to the flow field temperature profile boundary conditions. For example, the life of turbine buckets mounted on a turbine wheel is a function of not only the average temperature to which the buckets are exposed but to the temperature distribution of the gas stream seen by the buckets. As will be appreciated, a hot gas stream of combustion products flows through nozzles and then the buckets of the various stages of a turbine. Typically, the hot gases of combustion ate cooled by a cooling medium ejected into the hot gas stream through multiple orifices in the nozzle vanes. The orifices may be located along the leading edges, as well as the suction and pressure sides of the nozzle stator vanes, and conventionally are interspersed between the hub and tip portions of the nozzle vanes.
Flowing cooling air through orifices such as in nozzle stator vanes is a conventional method used to control the metal temperature and life of the part containing the orifices. That is, designers of parts exposed to extreme conditions such as the high temperatures of the hot gas path in a gas turbine normally control local part life by providing orifices in that part and flowing a cooling medium through the orifices and about the part. The life of parts downstream from the part containing the cooling medium orifices is typically not considered in efforts to cool the upstream part.
In accordance with a preferred embodiment of the present invention, the life of a downstream part exposed in a hot gas stream is in part controlled by changing the location, configuration or direction of the flow of the cooling medium through the orifices, or by changing the properties of the cooling medium, such as mass flow and coolant temperature, to alter the temperature distribution of the flow field affecting the downstream part to enhance its part life. For example, the cooling medium ejected through orifices in an upstream part creates a flow field with a particular temperature distribution surrounding the downstream part. The downstream part life is affected by the resulting temperature field. Consequently, by locating, configuring or directing the flow of the cooling medium through the orifices, the temperature distribution of the flow field affecting the second part can be favorably altered to increase its part life. That is, the temperature distribution affecting the life of the downstream part is enhanced by appropriate design of the upstream injection characteristics of the cooling medium into the gas stream.
More particularly, in the case of a stage of a turbine where the nozzle vanes have orifices for flowing cooling medium into the hot gas stream, the location, configuration and/or direction of the orifices are changed to provide a desired temperature distribution of the flow field downstream in which the second part is situate to enhance the part life. For example, leading edge orifices of the nozzle vane can be directed generally radially outwardly whereby the temperature profile distribution of the gas flow seen by the downstream buckets is lower at the bucket tip than at the bucket hub. With orifices directed generally radially inwardly, the converse is true, i.e., the downstream temperature profile becomes hub strong. The effect is more pronounced because the primary stream flow has low momentum in the area of cool air injection. As a consequence, the downstream parts, e.g., buckets, are exposed to a temperature profile distribution amenable to enhanced part life. Many other useful applications will occur to those of skill in this art, including sizing end wall purges for leakages to manipulate the temperature seen by downstream parts.
As a further example of controlling the life of a downstream part exposed in a hot gas stream, the properties of the cooling medium such as mass flow and coolant temperature can be changed. Rather than change the location, configuration or direction of the flow through orifices, the flow through the orifices can be changed to alter the downstream part life. Temperature flow through the upstream orifices can be changed, for example, by supplying the cooling medium from a different stage of the compressor. The life of the downstream part may thus be enhanced, while maintaining adequate cooling of the upstream part. Mass flow through the upstream orifices likewise can be changed, with similar results.
In a preferred embodiment according to the present invention, there is provided in a method of enhancing the life of a second downstream part exposed in a gas stream having a cooling medium injected therein through multiple orifices in a first part upstream of the second downstream part, comprising the steps of (a) ascertaining a temperature distribution of a flow field of the gas stream affecting the part life of the second part and (b) changing the location, configuration or direction of flow of the cooling medium through the orifices to alter the ascertained temperature distribution of the flow field affecting the second part thereby to enhance the life of the second part.
In a further preferred embodiment according to the present invention, there is provided a method of enhancing the life of a second downstream part exposed in a gas stream having a cooling medium injected therein through multiple orifices in a first part upstream of the second downstream part, comprising the steps of (a). ascertaining a temperature distribution of a flow field of the gas stream affecting the part life of the second part and (b) changing a flow characteristic of the cooling medium including, by altering one of the temperature and mass flow of the cooling medium through the orifices to alter the ascertained temperature distribution of the flow field affecting the second part thereby to enhance the life of the second part.